1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a circuit configuration of a program circuit programming specific information in a non-volatile fashion.
2. Description of the Background Art
In a memory device, if a defect is caused in a circuit of a memory cell array, the defective circuit is replaced with a redundant circuit provided in advance on a chip.
As such a defect saving method, a method has been adopted in which at least one of a spare row and a spare column is provided in a memory cell array and a memory cell that has become defective due to a defect caused therein is replaced with a spare memory cell on a column to column or row to row basis, each as a replacement unit.
In this method, a necessity arises for, when an address at which a defective memory cell is selected is inputted, the defect address is switched to an address of a spare memory cell. For example, for performing the switching, defect address information, which is an address of a defective memory cell, is in advance programmed using a program circuit in a nonvolatile fashion to perform coincidence comparison of the defect address with an inputted address and according to a result of the comparison, a spare memory cell can be accessed.
Examples of such a method to program defect information include (1) an electric fuse method in which a high voltage is applied externally to blow a fuse, and (2) a method in which a fuse is blown by a laser beam illumination. In recent years, the second method has been widely used as a general method since a fuse and a program circuit thereof are easy in layout, and large in design flexibility, thereby realizing a low cost.
FIGS. 5A to 5C are conceptual diagrams showing the method in which a fuse is blown by a laser beam illumination.
Referring to FIG. 5A, here is shown a method in which a fuse 121, made of wiring material such as aluminum, polysilicon and copper (Cu), and having a width of the order of 1 xcexcm and a length of 10 xcexcm is illuminated with laser light so as to cover a region 120 having a width larger than the fuse 121, thereby disconnecting the fuse 121. Note that hereinafter this method is also referred to as a laser trimming method.
According to the method, as shown in FIG. 5B, a fuse is illuminated by a laser to selectively disconnect it and to thereby program defect address information. In a case where a fuse is blown according to the laser trimming method, an energy dose of a laser beam is optimized, a shift of the laser beam spot from a target is controlled and other techniques are applied for sure disconnection of the fuse. In a mass production process, however, there arises a situation where a disconnection defect, that is a small connected portion, left in a fuse after fuse disconnection (hereinafter also referred to as xe2x80x9cmicro-shortxe2x80x9d) generates in a circuit.
FIG. 5C is a conceptual diagram showing the micro-short. When such a disconnection defect is present, a small leakage current flows in a program circuit, leading to a possibility of inconvenience that a normal memory cell and a spare memory cell are simultaneously selected in a memory device.
The present invention has been made in order to solve the problem as described above and it is an object of the present invention to provide a semiconductor device capable of removing disconnection defect due to micro-short to stably perform a coincidence comparison operation.
A semiconductor device according to an aspect of the present invention includes a plurality of internal circuits and a program circuit. The program circuit stores prescribed information required in at least one of the plurality of internal circuits in a non-volatile fashion and performs coincidence comparison between the prescribed information and input information in a normal operation. The program circuit includes a plurality of program elements, an internal node, a voltage supply switch circuit and a select circuit. The plurality of program elements each transitions from its electrically conductive state to its electrically non-conductive state in response to an external input corresponding to the prescribed information. A signal indicating a result of the coincidence comparison is generated at the internal node. The voltage supply switch circuit supplies, to the internal node, one of a first voltage commonly used by at least one of the plurality of internal circuits and a second voltage different from the first voltage. The select circuit connects electrically at least one selected according to the input information among the plurality of program elements between the internal node and a fixed voltage. The voltage supply switch circuit supplies the internal node with that one of the first and second voltages, which is smaller in potential difference from the fixed voltage than the other in the normal operation, while coupling the internal node with the other of the first and second voltages which is larger in potential difference from the fixed voltage than the one in an operation test.
That is, in a semiconductor device of the present invention, the select circuit in the program circuit connects electrically at least one selected among the plurality of program elements between the internal node and the fixed voltage. The voltage supply switch circuit supplies the internal node with the first or second voltage which is smaller in potential difference from the fixed voltage than the other in the normal operation, while supplying the internal node with the first or second voltage which is larger in potential difference from the fixed voltage than the other in an operation test.
With such a configuration adopted, a main advantage of a semiconductor device of the present invention is that in an operation test, an electric field higher than in the normal operation can be applied to at least one of the plurality of program elements. That is, a disconnection defect in a program element can be removed to achieve perfect disconnection, thereby enabling stable execution of a coincidence comparison operation in the program circuit.
A semiconductor device according to another aspect of the present invention includes a plurality of internal circuits and a program circuit. The program circuit stores prescribed information required in at least one of the plurality of internal circuits in a non-volatile fashion and performs coincidence comparison between the prescribed information and input information in the normal operation. The program circuit includes a plurality of program elements, an internal node, a select circuit and a test voltage supply switch circuit. The plurality of program elements each transitions from its electrically conductive state to its electrically non-conductive state in response to an external input corresponding to the prescribed information. The internal node is coupled to a first voltage commonly used by at least one of the plurality of internal circuits to indicate a result of the coincidence comparison in the normal operation. The select circuit, in the normal operation, connects electrically at least one selected according to the input information among the plurality of program elements between the internal node and a fixed voltage. The test voltage supply switch circuit, in an operation test, connects electrically each of the plurality of program elements regardless of the input information between a second voltage that is commonly used by at least one of the plurality of internal circuits and a fixed voltage. A potential difference between the second voltage and the fixed voltage is larger than a potential difference between the first voltage and the fixed voltage.
That is, in a semiconductor device of the present invention, the select circuit in the program circuit connects electrically at least one selected among the plurality of program elements between the internal node and the fixed voltage. The test voltage supply switch circuit, in an operation test, connects electrically each of the plurality of program elements to the second voltage larger in potential difference from the fixed voltage than the first voltage.
Therefore, an advantage of a semiconductor device of the present invention is that, in an operation test, an electric field higher than in the normal operation can be applied to the plurality of program elements. That is, a disconnection defect in a program element can be removed to achieve perfect disconnection, thereby enabling stable execution of a coincidence comparison operation of the program circuit.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.